Failure of cemented total hip arthroplasty (THA) often occurs when microcracks coalesce into a clinically observable failure. Considerable researches have focused on reducing stress risers in the devices' stem, on failures at the cement interfaces, and on failure in the cement mantle. However, it is not clear what role of progressive microcrack formation play in fatigue failure of a cemented femur stem construct. [unreadable] [unreadable] Our recent studies revealed that the acoustic signatures of model construct permit categorization of the fatigue induced microcracks into two types. Most Type I microcracks are identifiable under SEM with high signal energy. Type II microcracks are associated with low signal energy. The formation, accumulation, and [unreadable] distribution of Type I microcracks correlate with specimen failure whereas Type II microcracks seems to have a counter-correlation with failure. [unreadable] [unreadable] The next step forward in this avenue of investigation is to further study the correlation between these microcracks and material strength, and fatigue failure mechanisms. To achieve this objective, we will use newly developed acoustic emission microcrack source location technique in following steps. (1) We will characterize microcracks in bone cement and investigate their effects on the flexural strength of the cement. (2) We will characterize microcracks generated at the stem-cement interface and investigate their effects on the shear strength of the construct. (3) We will characterize microcracks generated in fatigue tests of cemented femur stem construct using cadaver specimens and correlate their presence with SEM observations. We will use quantitative indicators to assess the formation and progression of microcracks under various fatigue loading conditions. We will measure the onset time, distribution, density, and progression of these microcracks. The accomplishment of this objective will enhance our understanding of [unreadable] femur construct fatigue failure mechanism and open novel approaches to the studies of THA loosening. In the proposed work, we will test the following hypothesis: [unreadable] Two types of microcracks initiate in the cemented femoral stem constructs of total hip arthroplasty before clinically observable failure occurs. Type I microcracks directly contribute to the loosening of a femur stem constructs. Type II microcracks function as energy absorbers and thereby retard the loosening process. [unreadable] [unreadable] [unreadable]